The invention relates to a method for filling a retarder with an operating fluid by means of valve devices which are connected to a reservoir vessel with a reservoir air pressure Pv, and which feed an operating fluid with a control pressure Py into the retarder, in which case, after the retarder is switched on for a first time period T1, an overshoot control pressure Py(O) which lies above the rated pressure PyRATED for the rated braking torque which is to be set is set and, in a second time period T2, the overshoot control pressure Py(O) is reduced to the rated pressure PyRATED.
In addition to the method, the invention also specifies a control device for carrying out the method.
The braking torque of a hydrodynamic retarder is generally configured in such a way that, at the request of, for example, the driver of a vehicle, the working chamber is filled with working fluid or operating fluid, preferably oil or water.
In order to minimize the switch-on time of such a hydrodynamic retarder, it is necessary to fill the working chamber between the rotor and stator with the operating fluid rapidly, that is to say to feed the operating fluid out of a reservoir chamber into the working chamber at a high speed. This is usually carried out using a compressed air valve device whose output pressure Py, which corresponds to the control pressure of the retarder, feeds the operating fluid into the working chamber.
In order to ensure rapid switching on, it is known to override the setpoint control pressure or rated control pressure which is predefined by the desired rated braking torque. This means that for a short time period a higher pressure than the rated pressure is exerted on the operating fluid. It has become apparent that under certain operating conditions such actuation leads to the braking effect occurring only after a delay or, in an extreme case, causes the antilock brake system of the vehicle to be triggered.
A control device as described above for a retarder is known, for example, from DE-A-41 13 539.
The control device for a retarder according to DE-A-41 13 539 comprises a collecting tank, which has a fluidic connection to the retarder, and a pressure-setting component, which can have an atmospheric connection to the collecting tank, in order to impose a predetermined limitation on the compressed air flowing into the collecting tank, in accordance with the respective specified pressure level which is generated in the retarder.
The object of the invention is to overcome the above-mentioned disadvantages of the prior art.
This object is achieved in that the overshoot control pressure Py(O) and the time period, which is divided into the time periods T1 and T2, are specified or set as a function of at least one of the following variables:
retarder oil temperature
retarder rotational speed or vehicle velocity
vehicle lateral acceleration
ABS signal
axle load
brake-pause interval
brake fluid level
outside temperature
speed of the actuating element
acceleration of the setpoint value settings (variation in speed without setpoint value dynamics).
It has become apparent that it is particularly preferred if the level Py(O) and time periods T1 and T2 of the overshoot control pressure decrease as the retarder oil temperature rises.
In a developed embodiment of the invention, the retarder rotational speed is taken into account in that the level Py(O) and time periods T1 and T2 of the overshoot pressure decrease as the retarder rotational speed and/or vehicle velocity increase.
The preceding brake requests, for example the time period of the brake/pause intervals or the retarder braking level and the retarder braking level actuation velocity can also influence the configuration of the retarder braking torque. A further variable which influences the switch-on behavior of the retarder is the operating fluid level, i.e. the level of working fluid, for example that of the oil in the reservoir vessel. The time period for which the overriding is carried out and the level are predefined as a function of the operating fluid level which can be determined by means of sensors, the level Py(O) and the time period T1 and T2 increasing as the operating fluid level decreases. It is therefore advantageous if these a variables are also taken into account in determining the configuration of the overshoot pulse.
In the previously described method, the invention also makes available a retarder control unit for carrying out the method; said retarder control unit comprising an arithmetic unit, a control pressure-setting device and sensor devices for sensing at least one of the following variables:
the retarder oil temperature,
the retarder rotational speed,
the vehicle lateral acceleration,
the ABS signal and
the axle load
brake-pause interval
brake fluid level
the outside temperature
the speed of the actuating element
the acceleration of the setpoint value settings (variation in speed without setpoint value dynamics), and the retarder control unit is defined in that the arithmetic unit actuates the control pressure-setting device as a function of the sensed signals, in such a way that an overshoot control pressure of a predetermined level or value is set for a predetermined time period.